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50 DESIGN007 MAGAZINE I NOVEMBER 2022 Article by Anaya Vardya AMERICAN STANDARD CIRCUITS Introduction One of the biggest challenges facing PCB designers is understanding the many cost driv- ers in the PCB manufacturing process. is article is the latest in a series that will discuss these cost drivers (from the PCB manufactur- er's perspective) and the design decisions that will impact product reliability. Final Finishes e primary purpose of a final finish is to create electrical and thermal continuity with a surface of the PCB. Final finishes provide a surface for the component assembler to either solder, wire bond, or conductively attach a component pad or lead to a pad, hole, or area of a PCB. Another use for final finishes is to provide a known contact resistance and life cycle for connectors, keys, or switches. ere are a number of final finishes in use in the industry today, including: • ENIG (electroless nickel, immersion gold) • ENIPIG (electroless nickel, immersion palladium, immersion gold) • ENEPIG (electroless nickel, electroless palladium, immersion gold) • ImmAg (immersion silver) • ImmSn (immersion tin) • Sulfamate nickel/hard or so gold (electrolytic nickel/gold) • HASL (hot air solder leveling) • SnPb (63/37 tin/lead) • LF (lead-free) • OSP (organic solderability preservative) Final finishes are pr imar ily application driven, so there are a number of considerations that should be part of any decision to choose a final finish: DFM 101 Final Finishes: ImmSn • Lead (Pb) tolerant or lead-free (LF) process • Shelf life • Flatness • Lead or ball pitch • Wire bondability • Lead insertion • Solder joint integrity • Corrosion resistance • Potential problems • Cost Lead (Pb)-Free Finishes Lead-free finishes are considered RoHS- compliant (< 0.1% BW of finish, for Pb, Hg or Cd) with the single exception of tin/lead HASL. e RoHS-compliant finishes include the following: • ENIG • ENIPIG • ENEPIG • ImmAg • ImmSn • Electrolytic nickel/gold • LF HASL • OSP

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